code: def protected_key(self) -> List[str]:
      if self._cached_key is None:
          self._cached_key = self._get_key()
          return self._cached_key
      else:
          return self._cached_key
  
file_path: hail/hail/python/hail/expr/expressions/indices.py
imports: from hail.typecheck import typecheck_method, anytype, setof
  import hail
  from typing import List
label_desc: Use image node_id 6 for calling the Indices obj's underlying member method code with example usage: obj.protected_key() and returns: self, self